New Challenger owner. It fired.....on one cylinder???

[dave r]

Hey guys,
I recently picked up a 96 Challenger from a guy that let it sit because it was said to have a fuse issue. I checked all the fuses and disconnected and reconnected all components and it seems I got farther than the last owner. Today, I finally changed out the old gas and tried to fire it up. With both plugs in, it would turn over for around 4 seconds and automatically shut off. It wouldn't start then but it would just quit cranking as if the computer knew something was wrong and automatically went into no start mode or something. Plugs are good and both get spark. I pulled the front plug and tried to start it. It fired up and would rev. All on just the one cylinder. When I had just the front one in, it wouldn't do that or even try to start. What in the world is with this thing that it'll run on just the rear cylinder and won't try on the other and will just turn over for a specified time with both cylinders hooked up??

The kids are excited as heck to get it out on the water once before winter hits here.

Thanks for any help!

Dave

 

[USAF_Pride]

Welcome to the forums. The first thing you need to do is a compression test. You only need a few things to get a 2 stroke to run; spark, gas, air, & compression. You have spark and air, which leaves gas and compression.

The compression numbers should be 135 or better. Anything less and you may need a rebuild. If compression is good, then it is a gas issue. Do you have single or dual carbs? Are your fuel lines gray and say "Tempo" on them? If so, you need to replace them immediately and then take the carb(s) apart and clean them as those gray lines deteriorate and put green gunk in the carbs which eventually results in a lean condition and your motor burning up.

 

[dave r]

I'll get out and check today but I think I recall all the lines being black and I'm sure it has 2 carbs. Comp check on a 2 stroke. How many times do I let it turn over? Never did a check on a 2 stroke. The funny thing is, when it fired up and ran with the front plug out, it was spitting the fuel and oil out the plug hole. When I put the plug back in and hook it up, the engine would turn over for the same exact amount of revolutions and then stop as if it was controlled by something on a timer. I'd push the start button, it would turn over for a few seconds without firing and then stop turning as if I took my hand off the button (which I didn't).

Love the user name. I'm active AF now and will be retiring this coming April.

Thanks for the help. Dave

 

[USAF_Pride]

Compression Check on a 2-Stroke:
1. Remove plug wires and ground on e-box posts
2. Remove plugs
3. Install compression tester
4. WOT (Wide Open Throttle) and crank it for a few seconds (or until the gauge stops going up).
5. Rinse and Repeat on the other hole.

Do it a couple of times and report back the numbers. Also, have you tried new plugs?

 

[dave r]

Just finished checking it all. I found the procedures on line. Sadly I didn't think it would be that simple but all is well. The rear cylinder that it runs on is around 125 and the front that it wont is around 135. I did check plug resistance and tried a few different ones. Even put the one from the rear in the front as it's known to work. No go. Strange that it will run on one cylinder and not the other or both. After you see the below statement, it's strange it even runs at all!

I didn't realize I was reading the beeps incorrectly. When I tried to start with everything hooked properly, it would crank for the 4 seconds and die. Then I would try again and it would only beep once. I thought it was the short beep but turns out it was the one long one. I could remove the key and replace it and it would try again and then beep again. I went into the adv diag mode and got the 2 short beeps. That indicates the MPEM not able to read the electronic circuit in the safety lanyard or the magnet is defective or that the wires at the DESS post connector are mixed up. Bummer. Off to check the wiring paths. Hopefully it's backwards but I'm leaning to the circuit from the MPEM or the magnet because the PO says it just stopped working one day and they never were messing with the wires.

 

[dave r]

This is strange as all heck. I tried playing with the DESS post because I am reading all over that it is common to go bad or corrode or it just is a crappy system. 4 second crank and then one long beep on second try. I wiggle the switch instead of pull it off and it tries the one time with the same results. At least I don't have to pull the DESS off completely now. I checked the DESS contacts by checking for continuity and for resistance on the 3 wires of the post. Between the black and the black with yellow stripe, I get .3 ohms which is under the 2ohm required in the 583/717 thread. I would hope they are the same in this arena. I read that the MPEM will kill the start and ignition circuit if there is a problem reading the connection with the DESS setup. Well, if you look at this video, I can start it and rev it when I pull the front plug out and leave it connected to the wire and out in the open. What in the world is going on here? It's even getting spark if you can see in the video!!! Why is it not firing and running with both plugs in???



Thanks
Dave

 

[Waterluvr]

One quick thing to try the plug boot threads on to the end of the wire snip the wire tie on the boot and back it off of there and trim off about 1/4 inch of wire and put the boot back on and try running it that way.

My '97 MPEM requires you to remove the DESS key and replace it on the post after five minutes to reset the system if the engine hasn't been running.

 

[dave r]

The plug has spark when it's out of the engine and hooked up to the plug wire as you see in the video. Obviously the other does too since it's the only one running the engine. I just wonder if it's internal to the engine or if it is a computer thing that maybe changes the timing of the one plug to keep it from starting or something. This setup just makes no sense at all. I see spark, the engine runs, I should be able to put the plug in, plug it up, crank and fire right up. I am boggled at this setup.

 

[Waterluvr]

Dave, the only way to have any idea how much secondary pulse output the coil on a CDI system has is to use a proper ignition tester like my Stevens Instrument pictured here. Just because you see a plug firing over a .022 plug gap doesn't mean it's actually able to ignite the compressed fuel air mixture in the head.


Trimming the wire on a problem cylinder is a known fix that overcomes resistance at a hot spot in that point of the circuit and restores continuity on the ignition pulse to the plug. Or in other words for 99% of the people that don't own a proper tester it takes about a minute and doesn't cost you anything to try.

If you're still having problems, you need a proper tester to isolate the ignition side of things it appears your MPEM is doing it's job and allowing both coils to fire.

 

[dave r]

Ah, so what your saying is, take the plug side of the plug wire, and cut back some of the wire under the boot and reattach to ensure good connection? It's worth a shot.

I just think it's funny this thing will run on one cylinder but not on both or even just the other.

Thanks for taking the time to help guys. The kids are anxious!

Dave

 

[dave r]

So, I was going to try that but I went ahead and put the front plug back in and removed the back plug. It cranked the 4 seconds and then died. I repositioned the key and got my 2 beeps so I tried it again for the heck of it. I have no clue but now it worked. It will run off the front cylinder with the rear plug removed just as it did for the cylinders the other way. The removed plug needs to be in ground contact with the engine though or it will die. So, I try and put the other plug in and start it......Nope. Run on one seems to be the motto here. Progress though. Here's to hoping it's something simple. I just ordered a new starter because this one seems a bit slow regardless. Maybe the starter draws too much power or turns over too slow with 2 holes plugged and it quits for lack of rotation? This is too old of a system to do that I think.

Dave

 

[Waterluvr]

Ok, progress! Do you have another battery handy you can charge and install in the boat? These MPEM's are very sensitive to low voltage issues and actually have built in thresholds to shut things down. It may actually be that simple, always charge the battery when needed with the cables unhooked from the boat so nothing can get crossed back to the MPEM.

I have a few more idea's to try after we know 100% there's a good battery in there, try another one or charge the existing one and have it load tested and we can keep at this. I would like you to test the stator and rectifier to make sure everything is all square there.

Poor kids, that has to be hard on them watching dad work on the boat all day long. -I recall those days

 

[dave r]

I hooked it up to my F350 with 2 batteries and used one of them with the truck running instead of that dead blue top. I know that battery in my truck is good. When using the trucks battery, I got loud beeps from the buzzer. When using the spare counter battery I had, I got no beeps. I know I'm using a good battery in the truck.

I considered checking the stator and such. I'm not an electrician at all so even reading the service manual, I don't know what I'm doing there. I'm more mechanical. My resto-mod hot rods are always waiting on the electrical part to be done.

When they first heard it run, they were jumping for joy. Do you know how hard it is to explain to a 5 and 8 year old that it's running but not right? My 9 year old understands or just plays along till I say it's good. The other two are just itching to get in the water. I am too actually.

Thanks

Dave

 

[Waterluvr]

I hooked it up to my F350 with 2 batteries and used one of them with the truck running instead of that dead blue top. I know that battery in my truck is good. When using the trucks battery, I got loud beeps from the buzzer. When using the spare counter battery I had, I got no beeps. I know I'm using a good battery in the truck.

I considered checking the stator and such. I'm not an electrician at all so even reading the service manual, I don't know what I'm doing there. I'm more mechanical. My resto-mod hot rods are always waiting on the electrical part to be done.

When they first heard it run, they were jumping for joy. Do you know how hard it is to explain to a 5 and 8 year old that it's running but not right? My 9 year old understands or just plays along till I say it's good. The other two are just itching to get in the water. I am too actually.

Thanks

Dave

LOL, the cardinal rule of Sea Doo's is NEVER EVER hook up a jump line or boost to the boat. It can cook things that are made from unobtanium these days (try and buy an MPEM for your boat they don't exist anymore).

Single known good battery on it's own in the boat only, then we can go from there.

 

[dave r]

Dang you. OK, I'll get on it.

Thanks
Dave

 

[Waterluvr]

Dang you. OK, I'll get on it.

Thanks
Dave

This thread will automatically go down in the forum history as an example of what not to do when diagnosing engine problems. Go get a marine starting battery, they have the correct resistance the charging side of things on these motors seem to like the best. Small price to pay if you didn't cook the MPEM, and it sounds like you got lucky and didn't.

Tiny little Rotax stator meet Ford F-350 dual system fed by a massive Leece Neville alternator!

 

[Danosll]

Something I found out the hard way 15 years ago on my skidoo with dess was that you need to run resistor plugs. And resistor cap . Had a simililar issue after I installed non r type plugs ( thought machine would actually run better). Brought back to dealer to have repaired under warranty ( thankfully brp dealer was a good friend didn't charge me). Bombardier published aTSB on it.
I had another ski doo RV245 that when was hot would only run on 1cyl when hot. And had to remove one plug to restart. Turned out to be crank seal. Your post just refreshed my memory. Good luck

 

[dave r]

It's fixed. I have no clue. I put a new battery in it and had the same results. I got mad and disconnected every connector and wire and cleaned them and reconnected with dielectric grease and it just fired right up. No clue. I wish I could take credit for the fix but "Christine" as I have dubbed the boat, just decided she wanted to live. We'll get her out and try her on the water. I hope the pump setup is up to par.

Thanks for the help guys.

Dave

 

[Waterluvr]

It was the battery all along Dave, those MPEM's and rectifiers are really picky about voltage and that is known to cause all kinds of grief on the DESS side of things. Getting it disconnected and allowing it to reset on proper voltage signals was your fix. Glad it's working now!

 

[dave r]

Strange because the PO had it die and wouldn't restart. Was having similar issues. He bought that blue top Optima Marine battery and no good. He tried and tried and gave up because he couldn't fit in the engine bay. The battery went bad over the year because he didn't keep it charged. His loss, my gain.

Now I know. Thanks! We're going on a vacation next weekend but are surely going to try and get it out on the water the weekend after. The kids are excited.

 

[Waterluvr]

Strange because the PO had it die and wouldn't restart. Was having similar issues. He bought that blue top Optima Marine battery and no good. He tried and tried and gave up because he couldn't fit in the engine bay. The battery went bad over the year because he didn't keep it charged. His loss, my gain.

Now I know. Thanks! We're going on a vacation next weekend but are surely going to try and get it out on the water the weekend after. The kids are excited.

I would bank on that battery having been bad right from the start than just from sitting for one years time, having been charged or not that doesn't kill a battery that fast unless it spends the winter outside frozen in an ice dam for 6 months having been left out and forgotten.

This is why charging and proper load testing is an absolute must to know the condition of a battery when in question, whether it's brand new or dredged from 20 years of manky boat bilge slime.

I stocked and sold Deka Marine batteries for years, had about a 3% failure rate annually on brand new batteries, it happens. Old school point ignitions and related components weren't affected nearly to the extent that CDI board controlled systems are by bad ones or those in marginal condition.